Underground and underwater tunnels serve many purposes. Tunnels have been and are used as: Aqueducts to provide cities with water; passageways through mountains for automobiles and railroads; sewer systems; and storage areas.
Multi-layered tunnels form the substructure of many large cities in the United States. These tunnels house subways, walkways, waterways, utility lines and sewer systems. In many cities the tunnels need to be repaired or replaced.
More recently, tunnels have been proposed for use in scientific experiments to study the essence of matter and energy. These tunnels will house large particle accelerators. The tunnels are needed for safety purposes and to isolate the particles for experimental control.
Tunnels were originally dug by hand. Timber was used to support the bore. Later, mechanical hoes and dynamite were used to excavate the tunnel bore. In many instances it is beneficial to line the tunnel bore. Lining the tunnel supports the bore, prevents cave-ins and flooding. In most cases, concrete linings have replaced timber to support and line the tunnel bore. The excavation and lining were originally done as separate operations.
Now, tunneling machines are capable of simultaneously and continuously excavating and lining tunnels. Most of these machines include four major components. The major components included are: (1) an excavator to bore the tunnel; (2) a excavation debris removal system; (3) a tunnel lining system; and (4) a liner material retrieval system.
Many of the modern machines employ rotary excavators. The excavators are driven by at least one motor. They are usually propelled forward and guided by a plurality of hydraulic thrusters.
Excavation debris removal is an important function of every continuous tunneling machine. The rate of debris removal is directly related to the rate at which a tunnel bore is dug. Moreover, a machine cannot perform without a properly functioning excavation debris removal system.
There are several excavation debris removal systems now in use. Examples of the systems include mechanical backlogs, conveyor belts and pressurized pipe systems.
All of those systems are helpful in removing excavation debris. Unfortunately, each of the systems require that the machine be stopped periodically to add additional debris removal equipment. For example, the pressurized pipe systems include telescoping pipes to accommodate the forward movement of the machine. However, when the telescoping pipe is fully extended the machine must be stopped to add new pipe.
Stopping the tunneling machine reduces efficiency and momentum. Furthermore, restarting the machine requires the excavator to overcome static torque when it engages the solid medium. The restarts occasionally cause the excavators cutting bits to fail causing further delays. Consequently there exists a need for a machine capable of reducing or removing the number of times the machine must be stopped.
Modern tunneling machines employ either segmented forms or slipforms in their tunneling lining systems.
Segmented lining systems included a plurality of individual forms. The forms are set up in series behind the excavator. Concrete is pumped in between the form and the excavated bore to form the tunnel's lining.
As the machine advances, the segmented forms farthest from the excavator are brought forward to the excavator. Those forms are placed immediately behind the excavator to and are attached to the form closest to the excavator. Additional equipment is required to move the forms from the positions farthest from the excavator to the closest.
The slipform lining systems include an outer and inner form. The outer form usually houses the excavator and other components of the machine. Also, the outer form is usually shaped to the bore excavated by the excavator. The inner slipform is shaped to the interior contours of the tunnel. Concrete is pumped between the inner and outer forms to form the tunnel's lining.
Most systems now in use include liner material retrieval systems. Many of the systems include pumps to bring liner material from a remote location to the excavation area. There the concrete is pumped into either the segment or slipforms.
This can be a difficult task. Concrete does not travel well over long distances through pipes. Hardening may occur and clog the pipe. The composition of the cement can be adjusted for proper flow. Such compositions can increase the time required for the concrete to cure.
Another liner material retrieval system includes conveyor belts. Conveyor belts move freshly mixed cement from a remote location to the head of the excavator. The concrete is then injected by either pumping or spraying into the forms.
Again the liner material must travel long distances to reach the most recently excavated area. Because the materials must travel great distances hardening is a problem.
Consequently there is a need for a better means of bringing lining materials to the excavation head for introduction into the forms.
Another problem with the present liner material retrieval is the need to add additional pipe or conveyors. Even with telescoping pipes, the machine must be stopped occasionally. Thus, the same stopping and restart problems associated with the debris removal system are also present with the material retrieval system.